Setting up a remote FTP server on windows 2003

Hi, i do have a Linksys ISR, windows 2003 enterprise edition and a Public IP address. I would like to setup an FTp site on the windows 2003 pc using my public IP. I successfully managed to do it over the LAN and both downloads and uploads are fine however when it comes to setting it up over the Internet i terribly misfire. I do not have any experience in setting up a public IP and i do not know how to configure it on the machine so that it's accessible over the internet.
any help will be more than appreciated.

I am not an expert on this subject, but have you opened up a specific port on the Linksys router for your remote FTP Client to get into the LAN and be forwarded to the FTP Server? My router requires this for an remote application to get into the network.

AFAIK the isp doesn't get involved with your IP in that way, but i couldn't state that as fact.
When you say 'terribly misfire' what exactly do you mean?
Does it reach the ftp site but not allow login?
Does it timeout trying to connect to the ftp site?
Are you using a proper ftp client or just your internet browser?
More info please.

I am using core ftp and its doing fine internally [within the Lan]. I setup the Public IP on the router today and pinging it from inside the Lan its okay. However when i tried pinging it from outside there was no feedback. My internet connection is fine, i enabled single port forwarding and Dmz. Still no access to the ftp including the IP. If the iP could be accessible from outside then i would have a real chance of accessing the ftp site thats my thinking.
One last attempt of the day was setting up core ftp client in an internet cafe and trying to make a connection; it failed. To that end am still open to ideas on how to overcome this challenge.

jobeard, i'll let the mispelling of my name slide, seeing as you supplied some useful info.

edit: OT, does Shields UP test all ports? I need to test my firewall as Azureus says its blocked, yet i've opened the port.
edit2: sorry, just clicked your Shields UP link and it goes to a page about browser refresh being diabled. Funny thing though, my 'back' button wouldn't work, but i could still refresh the page!?!? Whats this page for anyway, doesn't do much.